International Institute of Marine Surveying
RMS

Seacocks and fittings found when surveying yachts/motor boats.

1. Gate Valves
2. Traditional Cone Valves
3. Ball Valves
4. Marelon Seacocks
5. Skin Fittings
6. Tailpipes or hosetail fittings
7. Bond or not to bond to an anode on a GRP boat
8. General Advice


1. Gate Valves

Poor gate valve - siezed, single clipped, undersize hosetail Gate valve seacock siezed, single clipped with undersized hosetail for pipe. Replace with bronze seacock and bronze hosetail of correct size

These are typically found on older crafts. They generally are the least suited to marine applications. There is no way of telling visually if they are open or closed. Faults found are usually failure of the handles. Heavy corrosion of the bodies. Note if the handles spin too easily then they are probably not operating the gate. The gate seizes and forces the thread on the handle.  Further they have a habit of leaking due to the gate not closing fully from marine growth or limescale on heads outlets. Many of these valves are made from brass not bronze or DZR (De-zincification Resistant Brass)

Unless the gate valves are particually good quality which is rare but can be found on larger valves that are made from all bronze including the handles on small craft, the advise is often to replace.  They should never be replaced for another gate valve.


2. Traditional Cone Valves

`Blakes exploded seacock     Leaking blakes seacocks on a heads installation.

The two Blakes seacocks are installed on a inlet and outlet on a heads installation.  They are leaking because the cone is worn, scored or the dogging plate is not tight enough.

Usually made by ‘Blakes'. These are typically found on older crafts. They have proved to be resilient over the years and are made out of a good quality bronze (or newer ones out of DZR) together with fixings. They benefit from having a flange built into the unit and are less prone to breaking off than a ball valve skin fitting in the event of an object hitting them. However typical faults found are the lack of maintenance and seizure of the outlet on heads and dezincification of the bronze securing through hull bolts.

The valves need to be greased yearly.


3. Ball Valves

Corroded ball valve on an raw water inlet and filter.      Bronze ball valve seacock

The quality of these vary greatly. Many cheap ones are made of nickel coated brass and have mild steel handles which rust. The quality of the nickel coated brass bodies can be questionable and unsuitable for marine use, current ISO standards state they are suitable for 5 years. However they are the most commonly found seacocks on craft and benefit from being easy to use and identify whether they are open or closed.

When replacing these seacocks, the material should be bronze or DZR brass, (marked CR on the body of the seacock).  Avoid seacocks marked CW617N, these are high zinc content brass suitable for fresh water domestic purposes.


4. Marelon Seacocks

Marelon seacock installation  

Plastic or more accurately 'Glass Reinforced DuPont Zytel.  These seacocks have no issues with corrosion other than possible crevice corrosion on the stainless steelscrews securing them to the backing pads - which as they are screwed onto the skin fittings is not generally critical.  Forespars make skin fittings also.


5. Skin Fittings

Again the material should be bronze or DZR suitable for use.  Test by scraping to see if they have dezincification (pinking ot taking on a dark red hue) and hitting with a small hammer.


6. Tailpipes or hosetail fittings

Again the material should be bronze or DZR suitable for use.  Testing is more difficult as most of the fitting is hidden.  Often impossible to tell what material has been used. Pull and push the fitting with moderate pressure when the craft is out of the water.  Replace with bronze or DZR if showing signs of corrosion.


7. Bond or not to bond to an anode on a GRP boat

If the seacocks/hosetails are showing signs of corrosion, the first area to look at is what material is being used.  Replace with good quality bronze or DZR it is not usually necessary to bond the seacocks.


8. General Advice

All seacocks should be easy and positive to operate. They should show no sign of corrosion, the tailpipes should show no signs of dezicification. They can be tested if they open and close correctly whilst out of the water by pouring water through the pipe whilst the craft is out of the water. If the material of the seacocks is unknown (no mandatory marking scheme) they should be regulary inspected.  The hosetails should be the right outside diameter for the inside diameter of the pipe.  The worm drive (jubilee) clips shoulds be all 316 stainless.

 


 

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